Atmospheric pressure and wind summary

Syllabus Overview

  • Weeks 1-2: Composition and Structure of Atmosphere
  • Weeks 3-4: Solar Radiation, Energy Balance, Temperature
  • Weeks 4-5: Atmospheric Pressure and Wind
  • Weeks 6-7: Cloud Development and Precipitation
  • Weeks 7-8: Atmospheric Circulations, Pressure Distribution, Radar
  • Exam 1: March 6

Atmospheric Pressure

  • Definition: Pressure = Force per unit area
  • Units: Pascals (Pa), millibars (mb), inches of mercury (in Hg), pounds per square inch (psi)
    • 1 mb = 100 Pa
    • 1 kPa = 1000 Pa = 10 mb
  • Exists due to molecular collisions

Pressure Characteristics

  • Density and Temperature Impact: Increases in density or temperature increase pressure.
  • Vertical Variation: Pressure decreases with altitude; approx. half for every 5.5 km (3.3 mi).

Pressure Distribution

  • Isobars: Lines of constant pressure; drawn at intervals of 4 mb.
  • Pressure Gradients: Indicates strength of pressure changes.
    • Dense isobars = steep gradient (rapid change)
    • Widely spaced isobars = weak gradient

Wind Formation

  • Causes: Pressure gradients due to uneven distribution of air.
  • Pressure Gradient Force: Acts from high to low pressure, causing wind movement.

Forces Affecting Wind

  • Coriolis Force: Apparent force due to Earth's rotation; right in northern hemisphere, left in southern.
  • Friction: Slows wind, significant in boundary layer (up to 1.5 km in altitude).

Hydrostatic Equilibrium

  • Balance between vertical pressure gradient force and gravitational force.
  • Maintains stability in atmosphere, allowing for upward/downward motions alongside updrafts in storms.

Wind Dynamics

  • Friction Impact: Lowers wind speeds; negligible in upper atmosphere.
  • Geostrophic Wind: Wind patterns in upper atmosphere without friction; follows isobars.